Euseius gallicus Kreiter and Tixier

NovljanK, Monica, K, Tanja Bohinc, KreiterK, Serge, K, Ismail Döker & TrdanK, Stanislav, 2023, The indigenous species of predatory mites (Acari: Phytoseiidae) as biological control agents of plant pests in Slovenia, Acarologia 63 (4), pp. 1048-1061 : 1055-1056

Euseius gallicus Kreiter and Tixier

Euseius gallicus ( Figure 6) was first described by Kreiter and Tixier in 2010 based on the material collected from Prunus cerasus L. ( Rosaceae ) in Montpellier, France ( Tixier et al.

2010). Subsequent studies showed that its natural populations are widely distributed around

European countries including Slovenia ( Döker et al. 2014 ; Tsolakis and Ragusa 2017 ; Bohinc et al. 2018 ; Kreiter et al. 2020). This species was first found in Slovenia in Šempeter pri Gorici

(Primorska region) in 2017, on the blackberry ( Rubus fruticosus L.) leaves ( Bohinc et al. 2018).

In 2018, it was found in Sečovlje (Parecag) on the persimmon tree (Diospyros kaki Thunb.), in

Dragonja on the turpentine tree ( Pistacia terebenthus L.), and in Lucija on cucumbers ( Bohinc et al. 2019).

In general, the Euseius species are known as pollen-feeding generalist predators and belong to the type IV group ( McMurtry et al. 2013). These species are general feeders and can consume mites, thrips, plant sap, and pollens ( University of California 2022). In addition,

they can also feed and survive on plant tissues without causing economic damage, when their primary prey are absent ( Nomikou et al. 2003 ; Adar et al. 2012). Furthermore, due to the presence of more pollen, their populations increase and peak during the blossoming period of crops or other plants nearby in the absence of any arthropod prey ( Croft et al. 2004). Due to their role as a standing army on the plants before pest arrivals, they might be considered one of the most important components of IPM programs.

The larvae of Euseius spp. do not feed while the nymphs and adults are active predators.The color of nymphs and adult mites depends on their diet, can be red after feeding on red mites,

yellow after feeding on thrips, and white after consuming pollens. Except when feeding or molting, they usually avoid direct sunlight and move quickly. The development time from egg to adult is 6-10 days, and the females live around 30 days and produce up to 27 eggs depending on the variety of their diets. In a warm place like California, 8 to 12 generations per year can be reported ( University of California 2022).

Pijnakker et al. (2014) reported E. gallicus as a promising biological agent against western flower thrips in the greenhouses of cut roses in the Netherlands. In this case, F. occidentalis occurred in the greenhouse at a low number and resulted in visible cosmetical damage on cut roses. Due to the low number of prey, the other predatory mites such as P. persimilis failed to make good colonization and protect the plants. Euseius gallicus in combination with additional commercial pollen established a stable population even six weeks of the absence of the pest prey.

Van Houten et al. (2016) reported that the development time from egg to egg-laying female is affected by temperature. At 13 °C, the development takes 22 days with 1.1 eggs laid/day/

female, while at 25 °C, the development takes 5 days only with 3.6 eggs laid/day/female. The same source also reported that the oviposition rates of female E. gallicus are different depending on the diet. On T. lativolia pollen and the combinations of those pollens with the first instar of

F. occidentalis , the oviposition rates were the highest, which were reported at 3.85 eggs/day/

female. The predation of E. gallicus to the first instar of F. ocidentalis is recorded at 2.60 killed thrips a day, and the number declined close to zero kills a day when T. lativolia pollens were also available in their diet.